1. Field of the Invention
The present invention relates to an optically pumped solid laser.
2. Description of the Prior Art
Prior art examples of optically pumped solid lasers utilize a xenon lamp, a krypton lamp, or a semiconductor laser as their pumping light source.
The solid laser can be efficiently pumped by coinciding the oscillation wavelength of the pumping source with the absorption wavelength of the solid laser medium. A semiconductor laser is more effective as a pumping source than either of the lamp sources because the wavelength purity of the semiconductor laser is much higher than that of the lamp light source. Furthermore, the pumping density can be made higher when a semiconductor laser is used as the pumping source, resulting in higher efficiency of the solid laser.
On the other hand, it is well known in the art that when using a xenon or krypton lamp as the pumping source, a slab laser can be applied to increase power. In the slab laser, the laser beam propagates in the medium in a zigzag mode, such that high power can be obtained with a small laser medium.
The semiconductor pumped solid laser has been disclosed by U.S. Pat. Nos. 3,624,545 and 4,720,940, Japanese Patent Applications (OPI) No. 189783/1987, 27079/1988, 27080/1988 and 140889/1985 (the term "OPI" as used herein means an "unexamined published application"), and IEEE Journal, June 1988, vol 24-6.
Of the above-described conventional solid lasers, small solid lasers have been disclosed in the Japanese Patent Applications (OPI) No. 189783/1987, 27079/1988 and 27080/1988. These solid lasers are pumped with one semiconductor laser (hereinafter referred to as "LD") and therefore suffer from the difficulty that injection of the pumping light beam cannot saturate the solid laser medium. Use of a high power LD to inject a pumping light beam of higher intensity would result in a higher output, however, the high power LD is expensive and has a short life.
Recently, an LD pumped solid laser has been disclosed which is miniaturized by coating the resonator mirror on the ends of the solid laser medium, however, it also suffers from the difficulties described above.
In the semiconductor pumped solid lasers disclosed in U.S. Pat. Nos. 3,624,545 and 4,710,940, the solid laser medium is pumped by a plurality of LDs, thus providing high power. In this case, since the laser medium itself also becomes large or is required to be made large, the injection of this pumping light beam connot saturate the laser medium, and it is difficult to pump the laser medium uniformly. Since the laser medium itself is large, the laser medium has the thermal distribution non-uniformly, with the result that the laser oscillation is unstable.
As described above, in the lamp pumped solid laser, a slab laser may be employed for high power. In this case, coating the resonator mirror of the laser medium is not practical and, accordingly, it is necessary to provide an external resonator mirror. As a result, the laser system is unavoidably bulky, and adjustment of the mirror is rather difficult.
The aforementioned IEEE, 1988, vol. 24-6 disclosed one example of a solid laser that utilized a coated resonator mirror in the laser medium. The solid laser may be pumped with a plurality of LDs; however, it is a ring laser, and the laser with a ring resonator is different from a laser forming a reciprocating optical path.
On the other hand, Japanese Patent Application (OPI) No. 140889/1985 has proposed a monocrystal fiber laser. This laser is disadvantageous in that it is expensive and difficult to manufacture. Also, it is difficult to inject the pumping light beam into the laser medium with high efficiency.
In view of the foregoing, an object of the present invention is an optically pumped solid laser that is small, but is high in output power.
Another object of the present invention is an optically pumped solid laser that is low in manufacturing cost, high in reliability, and long in life time.